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There are two pieces of information that every participant needs to be able to gather. Though these measurements should ideally be taken on the equinox, it is acceptable to do them a day or two before or after in case of weather.
- The precise time of solar noon (UTC)
Solar noon is not necessarily 12:00 PM. It is the moment when the sun is highest in the sky. Because of time zones and daylight savings time, it's necessary to record the time using UTC instead of your own local time. The time should be precise to the minute.
2. The solar zenith angle at solar noon
2. The solar zenith angle at solar noon
The solar zenith angle is between the sun and a vertical line. It will look different depending on where you are.
Southern hemisphere
Southern hemisphere
In the southern hemisphere, the sun will be directly to the north at solar noon, casting a shadow due south.
Equator
Equator
On the equator, the sun is directly overhead at solar noon. There won't be a shadow to measure!
Your solar zenith angle is zero.
Northern hemisphere
Northern hemisphere
In the northern hemisphere, the sun will be directly to the south at solar noon, casting a shadow due north.
At solar noon, the shadow will be pointing directly towards your hemisphere's pole. At this point, the shadow will also reach its shortest length of the day.
If you are using a magnetic compass to find the pole, remember to account for magnetic declination! The magnetic poles are not the same as the geographic poles.
Additionally, every pair of observers needs to know the distance between their locations. In order to do that, participants must use a GPS service like Google Earth to find the precise coordinates (degrees and minutes of latitude and longitude) of where they made their measurements. This will make it possible to look up how far away they really are without having to measure it themselves.
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